The disclosure of Japanese Patent Application No. 2000-385821 filed on Dec. 19, 2000, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an oil pressure control apparatus of a continuously variable transmission for use in a vehicle, such as a motor vehicle or the like. More particularly, the invention relates to an oil pressure control apparatus that is suitable for use in a hydraulic control apparatus for controlling pulleys of a belt-type continuously variable transmission based on oil pressure and, more specifically, to an oil pressure control apparatus for controlling the oil pressure of a hydraulic servo for a friction engagement element that engages at the time of a start of the vehicle and the oil pressure of a hydraulic servo that applies torque to the continuously variable transmission though the use of one and the same pressure regulating device.
2. Description of the Related Art
A related-art oil pressure control apparatus for changing the oil pressure of a friction engagement element that engages at the time of a start of a vehicle, for example, a direct (input) clutch or the like, between the control pressure and the working pressure (range pressure) is disclosed in, for example, Japanese Patent Application Laid-Open No. HEI 10-246317. This apparatus has a neutral relay valve that is switched by a solenoid valve, and a control valve whose pressure is regulated by a linear solenoid valve. When a manual shift valve is switched from a neutral range to a drive range (Nxe2x86x92D), the oil pressure control apparatus supplies the control pressure regulated by the control valve to a direct clutch hydraulic servo via a predetermined port of the neutral relay valve, and controls the control pressure so as to gradually rise through the use of an accumulator, so that the direct clutch is smoothly engaged. Then, the apparatus switches the neutral relay valve so as to shut off the control pressure and supply the range pressure from the manual shift valve to the hydraulic servo, so that the direct clutch is held in an engaged state.
According to the above-described related-art control of the direct clutch, at the time of switching the manual shift valve from the neutral range to the drive range (Nxe2x86x92D), the control valve is controlled through pressure adjustment by the linear solenoid valve, and the direct clutch is engaged based on the control pressure, so that the vehicle can be smoothly started. The aforementioned linear solenoid valve is a dedicated valve for starting the vehicle. Therefore, separately from the linear solenoid valve for controlling the direct clutch hydraulic servo, it is necessary to provide a linear solenoid valve for controlling the oil pressure to be supplied to a secondary sheave hydraulic servo so that a predetermined torque capacity is given to the continuously variable transmission in accordance with the input torque. Therefore, since a plurality of linear solenoid valves are needed, the high price thereof increases the entire cost. Furthermore, the construction of the oil pressure control apparatus becomes complicated. Thus, the need for a plurality of linear solenoid valves impedes the size reduction of the continuously variable transmission and the cost reduction thereof.
Accordingly, it is an object of the invention to provide an oil pressure control apparatus of a continuously variable transmission in which a pressure regulating device can be used for various purposes, and therefore the construction is simplified so as to allow size and cost reduction.